Pig shooters helping to spread disease

Anna Salleh

ABC Science Online

Monday, 22 October 2007

Evidence suggests recreational hunters are illegally transporting feral pigs across Australia to shoot them for sport. But what are the consequence for the health of humans and farm animals? (Image: L Leung/University of Queensland)

Recreational hunters who move feral pigs across Australia illegally could help spread diseases like Japanese encephalitis and foot and mouth, says one researcher.

This illegal transport undermines plans to control such diseases, says Dr Peter Spencer of Murdoch University in Perth, who adds that the plans need to be improved anyway.

"There are upwards of 20 million of these [feral pigs]," says Spencer. "The disease threat from them is enormous."

Spencer says feral pigs carry diseases like Japanese encephalitis, which has already killed humans in Australia, and foot and mouth disease, which has affected farm animals internationally.

By analysing DNA samples of around 1000 feral pigs across Australia, Spencer identified several pig clans, populations that range over particular areas.

He says pigs in one clan don't naturally mix with pigs in another, which means a disease can be controlled if an infected clan is successfully wiped out.

But in research now discontinued due to lack of funding, Spencer found pigs from genetically different clans in the same area in Western Australia.

So how did they get there?

Mystery pigs

Spencer says that as feral pigs are a declared pest, need to be tagged and have travel papers, these ones must have been transported illegally.

Spencer says evidence suggests the pigs are collected from hundreds of kilometres away by recreational hunters who want to shoot them for sport.

"That's really sinister. From a biosecurity point of view this is frightening," he says.

"It doesn't matter what plan you have in action for whatever disease, if one of those pigs has that disease and it happens to be moved in the back of a truck across the Australian continent, then you will transmit that disease."

He says there should be better policing of illegal movement of feral pigs and offenders should be prosecuted.

How many feral pigs do you need to kill before there's a dent in the population? More than we think, scientists are finding (Image: P Pavlov/Invasive Animals CRC)

Spencer also says his findings suggest current emergency response plans underestimate the size of the areas that need to be culled when an infection takes hold.

He says one modelling exercise he was involved in showed a pig population ranged over 100,000 square kilometres.

Attempts to wipe out every feral pig in sight within a 2000 square kilometre area failed to make a dent in pig numbers.

"If this had been an attempt to control a disease outbreak it would not have worked," says Spencer.

Dr Mike Bond of Animal Health Australia, which draws up the emergency response plans, agrees the illegal transport of feral pigs is a threat.

"It's a nightmare," says Bond, who experienced the problem in his former role as chief veterinary officer in Western Australia.

But he says plans can't account for the illegal movement of pigs, and policing the problem is not realistic.

"You can't have policeman every 100 yards around these areas," he says.

"When it comes down to practical reality, that's a very, very difficult job," says Bond. "I'm afraid there are no easy answers."

But he agrees understanding the boundaries of pig clans is important.

"That's all new science," says Bond. "If that makes a contribution to our understanding of the way feral populations behave we'd really be very interested in that sort of research."

Bond emphasises that the emergency response plans for animal diseases are only guidelines and are often modified as more is understood about the epidemiology of the disease. He says this has been the case of the response to equine influenza.